linux-ext4 - Re: [Cluster-devel] [PATCH] fs: push sync_filesystem() down to the file system's remount

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Date:	Thu, 13 Mar 2014 16:28:23 +0000
From:	Steven Whitehouse <swhiteho@...hat.com>
To:	Jan Kara <jack@...e.cz>
Cc:	"Theodore Ts'o" <tytso@....edu>,
	jfs-discussion@...ts.sourceforge.net,
	Anders Larsen <al@...rsen.net>, cluster-devel@...hat.com,
	linux-mtd@...ts.infradead.org,
	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>,
	Petr Vandrovec <petr@...drovec.name>,
	codalist@...EMANN.coda.cs.cmu.edu, linux-cifs@...r.kernel.org,
	linux-fsdevel@...nk.org,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Evgeniy Dushistov <dushistov@...l.ru>,
	Kees Cook <keescook@...omium.org>,
	fuse-devel@...ts.sourceforge.net, reiserfs-devel@...r.kernel.org,
	xfs@....sgi.com, linux-nilfs@...r.kernel.org,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	linux-nfs@...r.kernel.org, Artem Bityutskiy <dedekind1@...il.com>,
	linux-ntfs-dev@...ts.sourceforge.net,
	samba-technical@...ts.samba.org,
	Adrian Hunter <adrian.hunter@...el.com>,
	linux-f2fs-devel@...ts.sourceforge.net, ocfs2-devel@....oracle.com,
	linux-fsdevel@...r.kernel.org,
	Phillip Lougher <phillip@...ashfs.org.uk>,
	linux-btrfs@...r.kernel.org
Subject: Re: [Cluster-devel] [PATCH] fs: push sync_filesystem() down to the
 file system's remount_fs()

Hi,

On Thu, 2014-03-13 at 17:23 +0100, Jan Kara wrote:
> On Thu 13-03-14 10:20:56, Ted Tso wrote:
> > Previously, the no-op "mount -o mount /dev/xxx" operation when the
>                                   ^^remount
> 
> > file system is already mounted read-write causes an implied,
> > unconditional syncfs().  This seems pretty stupid, and it's certainly
> > documented or guaraunteed to do this, nor is it particularly useful,
> > except in the case where the file system was mounted rw and is getting
> > remounted read-only.
> > 
> > However, it's possible that there might be some file systems that are
> > actually depending on this behavior.  In most file systems, it's
> > probably fine to only call sync_filesystem() when transitioning from
> > read-write to read-only, and there are some file systems where this is
> > not needed at all (for example, for a pseudo-filesystem or something
> > like romfs).
>   Hum, I'd avoid this excercise at least for filesystem where
> sync_filesystem() is obviously useless - proc, debugfs, pstore, devpts,
> also always read-only filesystems such as isofs, qnx4, qnx6, befs, cramfs,
> efs, freevxfs, romfs, squashfs. I think you can find a couple more which
> clearly don't care about sync_filesystem() if you look a bit closer.
> 
>
> 								Honza

I guess the same is true for other file systems which are mounted ro
too. So maybe a check for MS_RDONLY before doing the sync in those
cases?

Steve.


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